fix(ci): 修复PR #332合并后CI失败 - F811重复import + url_security单测魔数校验

- generation.py: 删除重复的shared.url_security import（保留video_processing向后兼容层）
- test_url_security.py: mock数据添加ID3魔数头，适配新增的文件魔数校验

apps/worker/worker_app/tasks/generation.py

@@ -460,8 +460,6 @@ def _verify_url_accessible(
     import urllib.request
     from urllib.parse import urljoin
 
-    from shared.url_security import UrlSecurityError, validate_url_safety
-
     from video_processing.url_security import UrlSecurityError, validate_url_safety
 
     # P0-1 SSRF 防护：请求前先校验 URL 安全性

tests/unit/test_url_security.py

@@ -233,7 +233,7 @@ class TestSafeDownload(unittest.TestCase):
         with unittest.mock.patch("urllib.request.build_opener") as mock_opener:
             mock_resp = unittest.mock.MagicMock()
             mock_resp.headers = {"Content-Type": "audio/mpeg"}
-            mock_resp.read.side_effect = [b"audio_data", b""]
+            mock_resp.read.side_effect = [b"ID3audio_data", b""]
             mock_resp.geturl.return_value = "https://example.com/test.mp3"
             mock_opener.return_value.open.return_value = mock_resp
             size = safe_download_file(
@@ -242,7 +242,7 @@ class TestSafeDownload(unittest.TestCase):
                 purpose="test",
                 allowed_mime_types=ALLOWED_AUDIO_MIME_TYPES,
             )
-            self.assertEqual(size, 10)
+            self.assertEqual(size, 13)
             self.assertTrue(os.path.exists(dest))
 
     def test_safe_download_file_stream_size_limit(self):
@@ -274,7 +274,7 @@ class TestSafeDownload(unittest.TestCase):
 
     def test_safe_download_bytes_returns_content(self):
         """safe_download_bytes 应该返回文件内容."""
-        test_data = b"hello world test audio"
+        test_data = b"ID3hello world test audio"
         with unittest.mock.patch("urllib.request.build_opener") as mock_opener:
             mock_resp = unittest.mock.MagicMock()
             mock_resp.headers = {"Content-Type": "audio/mpeg"}